Using value sources on a multi-valued field can result in an exception if no data

Details

Description

SOLR-2522 Introduced the ability to reference a multi-valued field with doc values in a function query (value source) such as like this (an example using it for sorting): sort=field(myMultiValField,min) asc. In the event that the document has no values for this field, this feature behaves nicely in the aforementioned example. And it does if you reference in a 'fl' (as a DocTransformer): fl=id,myMultiValField:field(myMultiValField,min). In that case, the returned document simply doesn't have a name-value pair. But, if you sort on a more complex function that incorporates this, then you get an ArrayIndexOutOfBoundsException. Such as this:sort=sum(otherField,field(myMultiValField,min)) asc There may be other conditions where this same exception will be thrown; not sure.

The root cause can either be considered one of two things (or both) I think:

The longVal, intVal, etc. methods on FunctionValues need to be prepared for the possibility that the document has no data, in which case it should return a default value. This means TrieLongField (& friends) are erroneous.

ValueSource.ValueSourceComparator could/should call exists before calling doubleVal in the various methods where it does.

A workarround for Solr 5.3 users that should work in any situation is to wrap the field function in a def function since that forces an existence check before attempting to access the value (ie: use sort=def(field(mult_field,min),0)+asc instead of sort=field(mult_field,min)+asc)